I would not necessarily expect it but I appreciate it in a "systems" language where "systems" is defined as compatible with the existing traditional systems software on a machine. For example, it's nice if the stdbuf(1) command works on Rust binaries on glibc systems, and it's nice if a Rust binary calling a C library that writes with printf (or vice versa) don't maintain two separate output buffers.

To me, Go is the systems programming language for a world untethered by existing platform compatibility (and so, for instance, writing Go libraries to be called from C is awkward, calling C libraries from Go incurs overhead, Go has its own concurrency model, etc.) and Rust is the systems programming language for use cases where you'd otherwise want to use C (really "the platform's native systems language," but that's C on all the major platforms) but you want a better language. I appreciate that they both exist and target these different use cases.

Is Go widely used compared to the others as a systems language at this point?

Over the years I’ve gathered that it’s more of a competitor for C# & Java rather than Rust & C(++).

Depends what you mean by "systems language" (many common definitions turn out to be equivalent to "drop-in replacement for the platform language," which makes the argument circular), but the choice of Go as an implementation language for Docker and Kubernetes puts it pretty firmly in the "systems language" space IMO. Container management requires more systems-level functionality than C# and Java are really geared towards (although you certainly could use them, perhaps with a tablespoon of FFI).

Uhm, docker is just a wrapper around linux's kernel features, plus image format. Image format being just bunch of tarballs that needs to be mounted by _something_ layer by layer.

You can write it any language that runs on OS with linux's kernel. There are similar things written and damn bash. Does that make bash a system language?

The original version of Docker was written in Python, and the original version of Kubernetes was written in Java, so your argument doesn't hold.

Would this be the part of my argument that doesn't mention Python (which I personally consider a systems language) at all? Or the part of my argument where I say, "you certainly could use them"?

It just means that golang isn't anything special when it comes to writing tools like these, and is in the same ballpark as python and Java (it's somewhere in between the two of them, better than python but worse than Java), and you'd have to use the same escape hatches in golang as them to implement those tools.

Well, writing to standard output requires interacting with an operating system, so it's not surprising that it requires `std`. You cannot write to standard output without knowing what operating system you are compiling for.

Worth noting however that `writeln` only needs `core`, and as long you can provide an implementation of writing to standard output (pretty much create a struct and implement `core::fmt::Write` trait for it), creating `println` macro is trivial.

An example of this: https://os.phil-opp.com/vga-text-mode/#a-println-macro